Patent application title: METHOD OF POLYMERIZING SILICONE FLUID

Abstract:

The present invention relates to an improved method of polymerizing
silicon fluids, more particularly, this method is particularly convenient
for producing low viscosity silicone oils.

Claims:

1. An improved method of polymerizing silicone fluids comprising the step
of mixing one or more catalysts at ambient condition with silicones or
siloxanes and optionally heating, to effect rearrangement of chain length
of silicone molecules, wherein the catalyst is selected from the group
consisting of:Sulfurtrioxide (SO3),SO3 mixed with HMDSO to form
Bis(trimethylsilyl) sulfate,Bis(trimethylsilyl) sulfate,Sulfurtrioxide
containing siloxane,SO3 and H2SO4 mixed with HMDSO or any
siloxane, oleum,Oleum mixed with HMDSO to form Bis(trimethylsilyl)
sulfate,Oleum containing siloxane, andOleum and H2SO4 mixed
with HMDSO or any siloxane.

2. The method as claimed in claim 1, wherein the amount of catalyst is in
the range of 500 ppm to 50000 ppm.

3. The method as claimed in claim 1, wherein the siloxane molecules are
polydialkylsiloxanes.

4. The method as claimed in claim 1, wherein the siloxane molecules are
polyalkylhydrogensiloxanes.

5. The method as claimed in claim 1, wherein the siloxane is
Octamethylcyclotetrasiloxane.

6. The method as claimed in claim 1, wherein the siloxane molecules thus
prepared are polyalkylhydrogensiloxanes.

7. The method as claimed in claim 1, wherein the siloxane molecules thus
prepared are polydialkylsiloxanes.

Description:

FIELD OF INVENTION

[0001]The present invention relates to an improved method of polymerising
silicone fluid. More particularly, the present invention relates to
preparation of low viscosity silicone oil by mixing or adding a catalyst
into mixture of siloxanes & (optionally) terminators at ambient
temperatures or at higher temperatures.

BACKGROUND OF INVENTION

[0002]Siloxanes are a class of organosilicon compounds with the empirical
formula R2SiO, where R is an organic group. Representative examples
are [SiO(CH3)2]n (dimethylsiloxane) and
[SiO(C6H5)2]n (diphenylsiloxane), where n is
typically >4. These compounds can be viewed as a hybrid of both
organic and inorganic chemical compounds. The organic side chains confer
hydrophobic properties while the --Si--O--Si--O-- backbone is purely
inorganic. The word siloxane is derived from the words Silicon, Oxygen,
and alkane. Siloxanes can be found in products such as cosmetics,
deodorant, water repelling windshield coatings, and some soaps. They
occur in landfill gas and are being evaluated as alternatives to
perchloroethylene for drycleaning. Perchloroethylene is widely considered
environmentally undesirable.

[0003]It is known that Silicone fluids are usually straight chains of poly
(dimethylsiloxane), or PDMS, which are terminated with a trimethylsilyl
group (or groups). PDMS fluids come in all viscosities--from water-like
liquids to intractable fluids. All of these are essentially water
insoluble. PDMS fluids may be further modified with the addition of
organofunctional groups at any point in the polymer chain. Silicone gels
are lightly cross-linked PDMS fluids, where the cross-link is introduced
either through a trifunctional silane--such as CH3SiCl3 giving
a "T-branched" silicone structure--or through a chemical reaction between
a Si-vinyl group on one polymer chain with a hydrogen bonded to silicon
in another. This chemical "tying" of siloxane chains produces a
three-dimensional network that can be swollen with PDMS fluids to give a
sticky, cohesive mass without form. Further, silicone elastomers are
cross-linked fluids whose three-dimensional structure is much more
intricate than a gel. In addition, there is very little free fluid in the
matrix. Fillers, such as amorphous silica, are frequently added to the
matrix to give greater reinforcement to the network and thereby increase
the strength of the product.

[0004]Silicone resins are more heavily cross-linked polymer networks that
are formed by the introduction of a predominance of tri- and
tetra-functional monomers, such as CH3SiCl3 The physical
properties of the finished silicone resin can be tailored to suit many
applications by varying the ratio of branched and linear siloxanes and
also the functional groups attached to the silicon.

[0005]It is known that silicone oil of various viscosities are
manufactured by polymerization of low molecular weight
polydimethylsiloxanes --((CH3)2Si--O)n-- in presence of
chain terminators like Hexamethyldisiloxane
(CH3)3Si--O--Si(CH3)3 or low molecular weight
trimethylsiloxy terminated polydimethylsiloxanes
(CH3)3Si--O--((CH3)2Si--O)n--Si(CH3)3.
The said polymerization is generally carried out by adding Potassium
hydroxide (KOH) or other catalysts to siloxane & terminator mixtures and
then heating to high temperatures generally (90° C. to 150°
C.).

[0006]Further more siloxanes containing Si--H linkage during
polymerization form branching/cross-linking in the chain, which render
the whole polymer insoluble. The said process is can also be accompanied
by the liberation of hydrogen, which can be a hazard. It is known that
methylhydrogen chlorosilanes can be hydrolyzed and condensed to obtain
silicone fluids retaining a high proportion of reactive hydrogen, but
typically they contain 1% or more of branch sites. The reactions are
often difficult to control, and the results are erratic (i) sometimes
producing useless gels or hard brittle solids instead of fluids, and (ii)
hydroxyl substitution on silicon (.tbd.SiOH) which leads to gelation.
This limits the usefulness of methylhydrogen siloxanes as starting
materials for polymer synthesis.

[0007]According, to very commonly used procedure polydimethylsiloxanes
--((CH3)2Si--O)n--, (wherein more than 50% of molecules
have n equal to 4 and 5] generally of viscosity 2 to 5 CP, are mixed with
chain terminators (hexamethyldisiloxane/Trimethylsiloxy terminated
dimethyldisiloxane) and KOH. Then the mixture is heated up 150° C.
and maintained for time period of up to 5 hours. Then the said mixture is
neutralized, filtered and then heated under vacuum to obtain non-volatile
Silicone Oil. The disadvantages of the said process are: [0008]KOH
being immiscible in the siloxane. [0009]The polymerization being carried
out at 150° C., hence it is difficult to use Hexamethyldisiloxane
(HMDSO) as a chain terminator because it has boiling point of
˜100° C. and tends to vaporize at the polymerization
temperatures. [0010]The said problem is even more acute when trying to
make PDMS of molecular weight less than 1250, wherein more than 10% of
HMDSO is required to be added into the siloxane mixture for
polymerization. [0011]Heating the silicone mass mixture involves usage of
energy.

[0012]According to US patent documents U.S. Pat. No. 6,344,533 B1 and U.S.
Pat. No. 6,284,859 B1 in polymerization processes catalysts such as
toluene sulphonic acid, sulphuric acid, phosphoric acid,
trifluoromethanesulphonic acid, trifluoroacetic acid,
aluminiumsulphatedihydrate, phosphonitrilic chlorides, ionic phosphazene
acid catalysts, which are solid under conditions, such as acid activated
bleaching earth, acid zeolites, sulphonated charcoal and others have been
used. However, these processes have some disadvantages. [0013]While
making silicone oil of less than 50 CP viscosity, if sulfuric acid is
used as catalyst the mixing has to be very vigorous to keep the insoluble
acid layer from separating out. [0014]Also, the said reaction being
carried out up to 100° C., the suitable material for construction
of such reactor, which can withstand up to 100° C. with acid
catalysts is also expensive. [0015]Other catalysts can introduce a
non-silicone compound into the silicone mixture, for example in the case
of toluenesulfonic acid, toluene is introduced into the silicone mixture,
and toluene being soluble in silicone oil, hence this has to be separated
by distillation.

[0016]Solid catalysts are generally suitable only for low viscous
polymerisations, as these have to be finally separated by filtration.
Also the mixing has to be good to ensure adequate contact with the
insoluble catalyst.

[0017]The above-said disadvantages have been overcome in the present
invention. In the present invention linear or straight chain
polysiloxanes can be prepared with very less or no undesired
branched-chain polysiloxanes or gels.

OBJECTIVES OF INVENTION

[0018]1. The primary objective of the present invention is to provide an
improved method to polymerize siloxanes with least branching.

[0019]2. Yet another objective of the present invention is to provide a
method of polymerising silicones fluid of low viscosity and/or higher
viscosity.

[0020]3. Yet another objective of the present invention is to provide a
method of polymerization silicones fluid of low viscosity of 1 & 1.5 cP.

[0021]4. Yet another objective of the present invention is to provide a
method of polymerization of high concentration of low molecular weight
straight chain siloxanes.

[0022]5. Yet another objective of the present invention is to polymerize
polyorganosiloxanes.

SUMMARY OF INVENTION

[0023]The present invention relates to a method of polymerising silicone
fluid, wherein SO3 is used in catalytic quantity 2 ppm to 200000 ppm
or 0.00020% to 20% by weight and mixed with siloxanes & chain terminator
siloxanes. Preferably the SO3 concentration is between 500 ppm to
50000 ppm. Then a reaction time of 15 minutes to 24 hours is allowed for
the mixture. The reaction time is even less than 15 minutes depending on
the quantity of catalyst added and final viscosities desired. The
reaction is carried out at elevated temperatures or more preferably at
room temperatures. After the reaction is over (close to equilibrium) the
oil is neutralized, then optionally [0024]a) filtered and then heated
under vacuum to obtain non-volatile silicone oil (in case of high viscous
silicone). [0025]b) Distilled in case of low viscous oil. [0026]c) or any
other treatment as desired by a person skilled in the art.

DETAILED DESCRIPTION OF INVENTION

[0027]Accordingly, the present invention relates to an improved method of
polymerising silicone fluids comprising the step of mixing one or more
catalyst with silicones or siloxanes and optionally heated, to effect
rearrangement of chain length of silicone molecules, wherein the catalyst
is selected from the group comprising [0028]Sulfurtrioxide (SO3)
or [0029]SO3 mixed with HMDSO to form Bis(trimethylsilyl) sulfate,
or [0030]Bis(trimethylsilyl) sulfate or [0031]Sulfurtrioxide containing
siloxane or SO3 & H2SO4 mixed with HMDSO or any siloxane
oleum or [0032]Oleum mixed with HMDSO to form Bis(trimethylsilyl)
sulfate, or [0033]Oleum containing siloxane or [0034]Oleum &
H2SO4 mixed with HMDSO or any siloxane

[0035]One aspect of the invention is to provide a method wherein the
amount of catalyst is in the range of 500 ppm to 50000 ppm.

[0036]One another aspect of the invention is to provide a method wherein
the siloxane molecules is polydialkylsiloxanes

[0037]Yet another aspect of the invention is to provide a method wherein
the siloxane molecules is polyalkylhydrogensiloxanes

[0038]Still another aspect of the invention is to provide a method wherein
the siloxane is Octamethylcyclotetrasiloxane.

[0039]One more aspect of the invention is to provide a method wherein the
siloxane molecules thus prepared are polyalkylhydrogensiloxanes.

[0040]Yet another aspect of the invention is to provide a method wherein
the siloxane molecules thus prepared are polydialkylsiloxanes.

[0041]Yet another aspect of the present invention, wherein catalyst and
siloxanes are mixed in order to obtain products, which are not
branched-chain polysiloxanes or gels, but linear or straight chain
polysiloxanes. Especially in the case of polymethyhydrogensiloxanes,
hydrogen terminated siloxanes & organofunctionalpolysiloxanes.

[0042]Yet one another aspect of the present invention is to provide a
process provides a way for rearrangement of Si--O--Si linkage in
siloxanes which helps to produce various viscosities/molecular weight
Organo functional siloxanes, as other than the Si--O--Si linkage which
gets rearranged, there are other Si--X bonds which gets least affected
during the polymerisation process. Where the X can be Carbon or halogen
or hydrogen radical.

[0043]Yet another embodiment of the present invention, wherein SO3 is
mixed with Hexamethyldisiloxane and other siloxanes is used instead of
SO3 as such.

[0044]Adding SO3 having disadvantage that it is difficult to handle a
catalyst. Therefore, sometimes, SO3 mixed with HMDSO to form
Bis(trimethylsilyl) sulfate to use as a catalyst.

[0045]Alternatively, a mixture of siloxanes, HMDSO and SO3
(preferably SO3 20% to 35%) may be used.

[0046]Or a mixture of siloxanes, other siloxane chain terminators and
SO3 (preferably SO3 20% to 35%) may be used.

[0047]Or a mixture of siloxanes, H2SO4 (preferably 1 to 2%) and
SO3 (preferably SO3 20% to 35%) may be used

[0048]Or a mixture of siloxanes and Oleum may be used

[0049]SO3 containing sulfonating compounds like oleum can also be
used in place of SO3 in all the above combinations for preparation
of catalyst, although SO3 is the preferred compound.

[0050]Then this Bis(trimethylsilyl) sulfate can be added as chain
terminator either in combination with other chain terminators or by
itself into polydimethylsiloxanes to obtain silicone oil of desired
viscosity.

[0051]These catalysts being stable can be prepared or procured and stored
easily for use in polymerisation. For the polymerization of silicones
containing Si--H functionality SO3 in siloxane mixtures is a
preferred catalyst.

[0052]The advantages of the disclosed invention are thus attained in an
economical, practical, and facile manner. While preferred embodiments and
example configurations have been shown and described, it is to be
understood that various further modifications and additional
configurations will be apparent to those skilled in the art. It is
intended that the specific embodiments and configurations herein
disclosed are illustrative of the preferred and best modes for practicing
the invention, and should not be interpreted as limitations on the scope
of the invention.

EXAMPLE--1

[0053]A siloxane mixture of 1000 gm Octamethylcyclotetrasiloxane mixed
with 12 gm Hexamethyldisiloxane. Evaporation loss test of feed material
indicated 100% evaporation loss. The viscosity of the mixture was
˜2 cP. SO3 vapours are passed over the above-mentioned
mixture. The mixture is left for 24 hours then the mixture is neutralized
with NaOH. The viscosity of the mixture was now ˜200 cP.
Evaporation loss test of sample indicated ˜12% evaporation loss.
This indicates that the molecular weights of siloxane molecules have
increased. Evaporation loss test: Keep 1 gm sample in a 60 mm diameter
glass Petri dish. Keep this dish in an oven for 45 minutes. The oven is
maintained at 150° C.

EXAMPLE--2

[0054]A siloxane mixture of 1000 gm Octamethylcyclotetrasiloxane mixed
with 9 gm Hexamethyldisiloxane. Evaporation loss test of feed material
indicated 100% evaporation loss. The viscosity of the mixture was
˜2 cP Bis(trimethylsilyl) sulfate is added to the above mixture.
The mixture is left for 24 hours then the mixture is neutralized with
NaOH. The viscosity of the mixture was now ˜200 cP. Evaporation
loss test of Oil produced, showed ˜12% evaporation loss, which
indicates that molecular weights of siloxane molecules have increased.
and viscosity is achieved. Evaporation test: Keep 1 gm sample in a 60 mm
diameter glass Petri dish. Keep this dish in an oven for 45 minutes. The
oven is maintained at 150° C.

EXAMPLE--3

[0055]SO3 is added to 50 gm Hexamethyldisiloxane. Then part of this
mixture is added to 1000 gm Octamethylcyclotetrasiloxane mixed with
Hexamethyldisiloxane. The viscosity of the mixture was ˜2 cP. The
mixture is left as is for 24 hours then the mixture is washed with water
and neutralized with aqueous NaOH. The viscosity of the mixture was now
˜200 cP. Evaporation loss test of Oil produced, showed ˜12%
evaporation loss, which indicates that molecular weights and viscosity of
siloxane molecules have increased. Evaporation test: Keep 1 gm sample in
a 60 mm diameter glass Petri dish. Keep this dish in an oven for 45
minutes. The oven is maintained at 150° C.

EXAMPLE--4

[0056]200 gm Bis(trimethylsilyl) sulfate is added to mixture of 1000 gm
Octamethylcyclotetrasiloxane. The viscosity of the mixture was ˜2
cP. The mixture is left as is for 4 hours. Then the mixture is washed
with water and neutralized with aqueous NaOH. The viscosity of the
mixture was now ˜5 cP. Evaporation loss test of Oil produced,
showed 33% evaporation loss, which indicates that molecular weights of
siloxane molecules have increased and viscosity is achieved. Evaporation
test: Keep 5 gm sample in a 50 ml glass beaker. Keep this beaker in an
oven for 60 minutes. The oven is maintained at 150° C.

EXAMPLE--5

[0057]1000 gm volatile siloxane mixture obtained from cracking 500 CP
viscosity trimethyl terminated silicone oil is taken. Evaporation loss
test of sample indicated 100% evaporation loss. 100 gm of this volatile
siloxane mixture is mixed with 80 gm HMDSO & 60 gm SO3 900 gm of
remaining volatile siloxane mixture is mixed with 10 gm of the above
mixture containing SO3. The viscosity of the mixture was ˜2
cP. The mixture is left as is for 24 hours then the mixture is
neutralized with Na-silanolate. The viscosity of the mixture was now
˜300 cP. Evaporation loss test of sample, showed 12% evaporation
loss. This indicates that the molecular weights of siloxane molecules
have increased.

EXAMPLE--6

[0058]SO3 is added to 50 gm Hexamethyldisiloxane. Then part of this
mixture is added to 1000 gm mixture of hexamethyldisiloxane &
Methylhydrogenpolysiloxane cylics. The viscosity of the mixture was
˜2 cP. The mixture is left as is for 24 hours then the mixture is
washed with water and neutralized with water washes. The viscosity of the
mixture was now ˜10 cP. Evaporation loss test of Oil produced,
showed ˜12% evaporation loss, which indicates that molecular
weights and viscosity of siloxane molecules have increased. Evaporation
test: Keep 1 gm sample in a 60 mm diameter glass Petri dish. Keep this
dish in an oven for 20 minutes. The oven is maintained at 150° C.

EXAMPLE--7

[0059]SO3 is added to 50 gm Hexamethyldisiloxane. Then part of this
mixture is added to 1000 gm Octamethylcyclotetrasiloxane mixed with
Hexamethyldisiloxane. The viscosity of the mixture was ˜2 cP. The
mixture is left as is for 24 hours then the mixture is washed with water
and neutralized with aqueous NaOH. Then the Gas chromatography analysis
of the mixture showed Octamethylcyclotetrasiloxane less than ˜1%,
and >50% of molecules having 3 to 6 Silicon atoms in their structure.
Hence producing high concentration of low molecular siloxanes.

[0060]In each example, SO3 is used either directly or indirectly as a
polymerisation catalyst.

Advantages of the Invention

[0061]1. SO3, Bis(trimethylsilyl) sulfate & other siloxane SO3
mixtures are miscible in silicone oil so the polymerization proceeds with
ease.

[0062]2. The reaction takes place even at ambient temperatures this leads
to energy savings & even the material of construction restrictions ease,
as many plastics are also suitable at ambient temperatures.

[0066]6. No impurity is introduced. In this process SO3 used is
neutralized and then the salt is separated by filtration or by washing or
can even be left in the mixture. The carrier siloxanes if at all used is
selected from the siloxanes similar to those that are to be polymerized
so these do not bring any unwanted impurity into the silicone
polymerizations.

[0067]7. Since polymerisation can be done at room temperatures there is
energy savings.